Conventionally, separable optical fiber ribbons have widely been utilized in order to achieve higher density and easy handling in optical glass fibers (hereinafter referred to as optical fibers) used as an optical transmission medium. A separable optical fiber ribbon is one in which a plurality of colored optical fibers arranged in parallel are coated with a collective coating resin so as to yield an optical fiber ribbon, and a plurality of such optical fiber ribbons arranged in parallel are further coated with a binding resin so as to be integrated. The separable optical fiber ribbon can be divided into individual optical fiber ribbon by tearing the binding resin apart at a predetermined part.
For making the separable optical fiber ribbon having the above-mentioned configuration, a plurality of colored optical fibers arranged in parallel are initially transferred at a predetermined line speed to a coating unit and a curing unit in succession, while a thermosetting or UV-curable resin is applied thereto and cured, so as to form a collective coating resin, thereby yielding an optical fiber ribbon. Subsequently, a plurality of optical fiber ribbons are arranged in parallel and are coated with a thermosetting or UV-curable resin, which is then cured, so as to form a binding resin, whereby a separable optical fiber ribbon is obtained.
When tearing apart the binding resin in thus obtained separable optical fiber ribbon in order to divide the latter into individual optical fiber ribbons, the colored optical fibers may be exposed from the collective coating resin or drop out therefrom if the adhesion between the collective coating layer and the colored optical fibers is insufficient. If the binding resin expands too much, on the other hand, it may be hard to tear apart and divide.
For overcoming such phenomena, various studies have been conducted concerning physical properties of resins to be used, and various separable optical fiber ribbons have been proposed. For example, Japanese Patent Application Laid-Open No. HEI 10-197767 discloses a separable optical fiber ribbon whose physical properties such as the adhesion between the collective coating resin and binding resin, the Young's modulus and extensibility of the binding resin, and the like satisfy predetermined conditions, while stating that such a separable optical fiber ribbon can be divided into the individual optical fiber ribbons easily and reliably.